I haven't seen the print edition of Newsweek, but according to Media Matters and Michelle Malkin (wow, there's a link you don't see here everyday) the cover is just one of three shots focusing on Sarah Palin's body. This is the image accompanying Christopher Hitchens' essay. You can read the Hitchens' piece (which I liked a great deal) and make of the pairing what you will.
From my humble vantage point, taken together, the focus on Sarah Palin's body is creepy, and yeah, sexist. I can't imagine them doing this with any male politician, no matter how devoid of ideas.
UPDATE: Wanted to give props to SapphireCate for the catch. And also promote this comment from Deborah, which says, what I could not:
We want to hear what you think about this article. Submit a letter to the editor or write to email@example.com.